pappyman

I use to have a Wells Cargo enclosed trailer that was 22 ft it was a tag along......Wells Cargo put a Bull Nose on the front of this trailer to improve the Areodynamics and I did notice it pulled the same way even with a strong head wind

Maybe this is something you should look into.......adding a Areodynamic sheild to the front of your trailer

BlueRam01

It seems like everyone is trying to help you with what is causing your areodynamic problem, mainly driving too fast and oversized tires. I know that's how I would have answered at first but know I have a different response.
Understanding the difference between the travel trailer and fifth wheel designs it stands to reason that with your travel trailer, you need to continue the air flow from the back of the cab to the leading edge of the trailer to reduce turbulence. The simplest method is the one you do not wish to entertain and that is the addition of a cap to the bed (on which you could add a wind deflector) or a hard tonneu cover.
So with those options off the table the only thing I could think of would be to try "Airtabs" from Geno's Garage. They are a bit pricey($2.50 each white, $3.50 each clear) but you could stick them on the cab roof and the trailer to see if it works. They are placed across the top and sides about 1 foot from the trailing edge spaced about a foot apart. They claim that a friend's brother-in-law's cousin got better milage with them . Who knows, it might fit with what you are trying to do. You might have to call them for more info or check page 24 of their Fall 2005 catalog.

pmtg

trailer brakes sticking???

darkvader

have you compensated for slower speedometer due to larger tires. both odometer and speedo will be slower. you may be running 115 miles and showing 100mi, may be goind 78 mph rather than 70 mph. larger tires are also spreadind rpm between shifts. if you cant lockout od its a problem. as for wind resistance best results are reducing the vacume behind trailer, search air tabs or draft a big truck
Clark

IsItFast

Well the tire size has been compensated for via a computer reprogram....it is about identical to the stock speed according to GPS. I will have to look into these Airtabs though. Anyone have a link?

xyzer

What RPM do you turn at say....70mph?

Thanks

IsItFast

Not sure about 70MPH but at 78 I am at about 1800.

I looked into the airtabs but I don't think they will work on my trailer since the sides are not flat....cool concept though. I may just go with a big wing.

Begle1

You're not supposed to get decent mileage for the first 15,000 miles, the engine isn't broken it yet!

Most people say that the efficiency goes up 2-4 MPG after 15,000.

1sttruck

Our trucks as delivered seem to be designed to tow max loads at 65 mph, as it typically ends up being about 2000 rpm, which is what Cummins notes as being the best rpm for load and mileage. Taller tires/gearing may produce better unloaded mileage at say 70 mph to 80 mph, but I'll guess that for many it'll be worse with a max load.

Heavy duty OTR trucks seem to often use deflectors to smooth the air flow from the cab to the front of the typically flat trailers that they tow. I think that the super-dooper-fast 1/2 ton Dodge has some aero tricks as it's rated for some fairly high speeds, so you could see what they used.

CoastalDav

Don't know if I should even get into this or not. Here some practical stuff that I have expierenced.

While driving on I-35 out of Emporia KS headed to Duluth, MN I encountered a 35-40 mph head wind. It lasted all day. I was towing a 35ft Fifth Wheel that was around 13,000lbs. The front of the trailer extends 5-7ft above the roof line of the truck. I was not able to drive the truck in 6th gear with this wind. I back off to fifth gear and the truck would maintain 60mph and was getting 7 mpg on the ECO function that shows what your getting as you drive. It also has an average mpg feature. (very usfull when towing)

My point here is, the gear ratio in Sixth is 2.58:1 in Fifth its 3.54:1

My relative speed into the wind was estimated at 90mph. I was driving 60.

My normal mpg is 11 at 65mph. (235hp stock cummins) (12-13.5 at 55-60)

If your tires are anywhere in the 31-32" diameter range I can believe what you say about the tire change in size not making any differance in the mpg. My 16" tires are 31.5" in diameter. A 225x70x19.5 Goodyear G124 is 32.4" in diameter. I have no figures for 22.5 tires not knowing the profile.

If your tires are 36-39" in diameter you have drastically changed the rear gear ratio of your truck. Go to www.ricksontires.com and check out their tire size/speedo/gear ratio calculator. You'll see there, they are saying with a 19.5 tire and a 3:73 rear you will be at 2:81:1 after the tire change. I don't know anything about the diameter of their tires or how the calculator is set up.

So there are two things here to consider.

Your driving habits (towing at 75-80mph) are creating a load like I had with the 35mph headwind. Thus, causing the low mpg. Your truck, not being broke in yet, also is contributing. I can tell you from my own expierence as some others have here, that if I pull my fiver at 75mph I too see 7-8 mpg in overdrive with that 2:58:1 ratio in 6th gear.

Gearing; if your tires are of normal diameter you should not see to much of a ratio change. If they are much taller, then you've created the problem not having enough mechanical advantage to pull the load. I would guess your EGT's are up while towing as well. You say there is no differance with the tires. If that is so;

Slow down and wait for you engine to break in. You should also see 11-13 mpg while towing.

Dave

FAY

Type truck air deflectors into Google and pick the first listing. I think it was called wind-tunnel-design.com and they have whatever you need.

rockhound

how nose heavy is the trailer, try raising the front end of the trailer

a trailer that is nosing down too much causes wind resistance and will pull very heavy. sort of like a spoiler you have a thirty foot long flat area that catches wind. if your trailer is just slightly nose high the only part that can catch wind is the front not the entire top of the trailer. try a shorter drop on your hitch or roll it over to raise it

trailer should ride about 2-4 inches higher in the front than the rear when being towed

1320

7 mpg.....is that a 30 ft high 5 th wheel?

I pull a 50 ft enclosed GN 11 ft high to the 2 roof airs, empty its 9600 lbs, loaded ussually 17500. I have a nv5600 conversion with 3.54 gears and a 235 85 tire. I get 12-14 loaded if I go slow at 64-69. To get 7 mpg.....you have a problem, either brakes, bearings, differential, trans, or tiresize to computer problems. I would think you would have smoke at 7 mpg, all the time.

The 5600 helped mpg a bit. The problem is going slow. It will tow at 75-80 no problem.

thumper 549

well glanced through your thread.....couple of things...1- good mileage at 75 to 80 ? never will happen
2- In the aerodynamic world the real culprit in drag coeificancy is the rear end not so much the front. Add a pc. that will bring it to a point back there (like the tail of a oil drip)
3- did anyone mention trailer axle alignment? most over looked issue in the trailer world -everyone assumes all is ok.......most are not

herb

i have an aerodynamic problem also. i pull a 48' goosneck with a sleeper built on it. i was thinking of adding a v nose to the sleeper and building it lower in the front (toward the truck )
Proably will get at it as soon as it returns from California